This work investigates alterations in activity or concentration of various enzymes and substrates of the brain in response to episodes of anoxia or hypoxia. Changes in content of water and electrolytes also are examined in cortex, basal ganglia, and hemispheral white matter. Tissues are examined during the course of the episodes of anoxia and hypoxia and also following resuscitation and recovery. A particular attention is paid to comparisons of changes in enzyme activities and substrate concentrations in brains of animals which develop brain edema and those which show normal recovery.